The invention relates to a windshield wiper device for wiping windshields, having at least one motor whose direction can be reversed and at least one wiper oscillating between two reversal points coupled to the motor, having a control device which switches the motor by means of switching signals and having operating signals supplied to the control device, where the control device determines the switching signals from the operating signals and thus the reversal points of the wiper.
Such windshield wiper devices are known, for example, from DE 196 34 559 A1. The operating signals which are supplied to the control device are dependent on motor current. The result is that if the motor binds, for example, it is possible to reverse the motor prematurely because of the high current draw of the motor. The drive elements can advantageously be designed to be small. The disadvantage of this state of the art is, however, that with identical switching signals the wipe pattern between the reversal points of the wiper is larger with a wet windshield surface because of the lower frictional resistance between wiper and windshield surface than with a dry windshield surface. To prevent the wiper from striking the A-pillar of a vehicle, for example, with a high degree of wetness on the windshield surface, the wipe pattern from the state of the art is designed such that it demonstrates a certain safety margin to the A-pillar with a wet windshield. The result of this is that the wipe pattern between the reversal points with a drier windshield surface can be smaller by about 5xc2x0 to 6xc2x0 than with a wet windshield surface.
The object of the present invention is therefore to prepare a windshield wiper device that optimizes the wipe pattern between the two reversal points of the wiper depending on the operating conditions of the wiper. Optimization can take the form of a reduction as well as an increase in the size of the wipe pattern.
This object is accomplished under the invention with a windshield wiper device of the type described above by providing the degree of wetness of the windshield surface as operating signals to the control device. The wipe pattern between the two reversal points can thereby be altered such that its size is always optimal, depending on the degree of wetness of the windshield surface. With a relatively dry windshield the wipe pattern can be enlarged in accordance with the invention; and reduced with a wet windshield because of the lower frictional resistance between windshield surface and wiper.
Advantageously the degree of wetness of the windshield surface is detected by a rain sensor. Modern vehicles have such a rain sensor to activate the windshield wiper device automatically, depending on the precipitation detected by the rain sensor. Under the invention the originally intended function of the rain sensor is expanded and is used to transmit operating signals to the control device.
In an advantageous aspect of the invention provision is made for signals dependent on vehicle speed to be supplied to the control device as additional operating signals. Because of the relatively high wind forces acting on the wiper, particularly at high vehicle speeds, the wipe pattern specifically between the two reversal points can be undesirably enlarged. The situation can occur that the wiper strikes the A-pillar, for example. Based on the operating signals identifying high vehicle speed, the wipe pattern between the two reversal points of the wiper can be reduced.
Advantageous provision can be made for vehicle speed to be detected by means of a speed sensor. Speed sensors are found in the speedometer units of vehicles, for example, so that the speed determined through the speedometer, for example, can be utilized directly or indirectly as an operating signal.
In another preferred embodiment of the invention, signals dependent on motor current are supplied to the control device as additional operating signals. Specifically in combination with the operating signals for the degree of wetness of the windshield surface and for vehicle speed, high frictional resistance between the wiper and the windshield can be recognized by detecting motor current. High load on the motor indicates higher frictional resistance between wiper and windshield, whereby the wiping angle can be corrected under the invention by enlarging it. Low motor load, on the other hand, indicates low friction between the wiper and the windshield surface, whereby a reduction of the wipe pattern between the two reversal points can be implemented by the control device.
An ammeter, for example, can be provided to determine motor current.
In another aspect of the invention, signals depending on motor over-run after it has been switched off, or after it reverses, are supplied to the controls as operating signals. Motor over-run unintentionally affects the wipe pattern between the two reversal points of the wiper. By detecting over-run, it is possible to reverse the motor earlier, so that precise correction of the over-run is possible.
Motor over-run can be detected advantageously by means of a counter. The type, construction and function of such a counter is known from DE 197 10 099 C2, for example.
Under the invention provision can be made for signals depending on wiper speed to be supplied to the control device as additional operating signals. Because of the inertia of the wiper and the linkage located between the motor and the wiper, for example, higher wiper speed results in increased flexibility in the windshield wiper device and consequently to an increase in size of the wipe pattern between the two reversal points. Using the appropriate control device, operating signals for higher wiper speed can consequently result in the wipe pattern between the two reversal points being reduced in size.
By using a suitable measurement signal it is possible to determine wiper speed. It is also conceivable that a motion sensor located on the wiper shaft can be used or that the switching signals which determine wiper speed are detected directly.
The object stated above is also achieved by means of a process to operate a windshield wiper device having at least one wiper oscillating between two reversal points, which is driven by a motor whose direction can be reversed, having a control device switching the motor by means of switching signals and having operating signals supplied to the control device, where the control device determines the switching signals from the operating signals and thus the reversal points of the wiper, the process being characterized in that the degree of wetness of the windshield surface is supplied to the control device as operating signals.
In addition to the degree of wetness of the windshield surface as an operating signal, signals are conceivable which are dependent on vehicle speed and/or motor current and/or motor over-run after the motor is switched off and/or wiper speed.
Advantageously the control device is adjusted to its base setting with the vehicle stationary.